Teach me about engine break in

[FORANE]

We're installing new ring sets on my Titan X-340. It has around 350 TTSN with Nickel carbide cylinders. It had some blow by and upon digging into it we found a broken ring. Because everyone likes pics,


Question is how to best do a break in on this motor. It will have NiC3 cylinders and CN203 nickel rings.
Titan has a break in procedure here:
http://www.continental.aero/xPublications/xService Bulletins/Experimental PMA/E-SB003/
Looks like the cliff notes are:
Limit ground runs
Keep CHT <= 400 F
Keep oil temp <= 200 F
Shallow climb out.
Maintain rich mixture.
Maintain 75% power for maximum amount of time during break in.
Avoid letting the prop drive the motor with low power setting descents.

Questions are:
Is above accurate and complete?
How exactly does one maintain 75% or greater power? Full throttle at or below what altitude?
Related to above question, how high or low may I or should I run RPM?
Would it be bad to make a first flight of only 20 minutes or so?
Understand this is in a Lancair. The airframe has low low drag. One cannot maintain significant power on and slow down while descending for landing. Given that, would it be better to just make a first flight cross country on a 2+ hour flight?

Other question, any ideas why a ring would have broken in the first place?

 

[catmandu]

"The above" is accurate, complete, and open to slight interpretation. Slight deviations from optimum have to be accommodated in the big scheme of things. I like to do at least one hour for the first flight in similar scenarios.

Lycoming designed engines to run with all levers forward up to TBO. Not very efficient, but you can do it. When we were dealing with a fresh overhaul in the partnership, we waived the $30 hourly reserve fee to encourage levers forward.

You have to do your own risk management, but my personal opinion is that descent and pattern power are more risky long term than the options altitude provides in the near term. I'd fly low, JMHO.

The rings broke because the hangar fairies broke in and fargged with your motor (don't have an answer for that, sorry.)

 

[Magman]

“ Limit ground runs” can include towing rather than a downwind taxi.

 

[Salty]

Ring couldn’t float due to carbon and varnish so it broke.

fly it hard and cool (fast) at lowish altitude

personally, I did laps above a towered airport at hp varying from 75 to 100% at 3000 feet MSL full rich.

 

[chemgeek]

I run my engine hard (75% power ideally) until oil consumption stabilizes, which is usually only a few hours. I keep straight mineral for a full 10 hours, then switch to my usual multi weight oil. Worked well for many cylinders as well as an overhauled engine. Of course the supplier will have specific recommendations, but they are usually more or less the same.

 

[Daleandee]

Ring couldn’t float due to carbon and varnish so it broke.

Could be. Only other thing that comes to mind is the ring gap set too tight during the engine build. Pretty unlikely but even the best can make a mistake.

 

[Magman]

Not that unlikely.

O-290D2 with all cylinders with broken rings.

“Choke “ cylinders and we believe gaps were too tight.

I used to like getting a jug with loaded pistons.

Now I pull apart .

“ Trust but verify”.

 

[FORANE]

I have been researching the possible causes of broken rings and found some possible etiologies.
What @Salty and @Daleandee stated plus detonation, metal fatigue, manufacturing defect, overheating, and then there's this:
The Titan service letter for ring installation comes with this bold warning:
http://www.continental.aero/xPublications/xService Bulletins/Experimental PMA/SIL004/
WARNING
Hard bumping of the piston ring during installation can cause
the formation of cracks in the piston ring that may not fail
immediately; however, piston ring breakage can introduce
pieces of the ring expander between the piston and bore. This
can result in the formation of grinding type cracks on the bore
surface and may cause complete catastrophic engine failure.

Piston ring flutter is another possibility. As slippery as this plane is, I do occasionally close the throttle and flatten the prop pitch in descent. If I haven't done that in descent, it is always done in the pattern or prep for landing. I found some mentioning this practice as bad such as here:
https://forum.cubcrafters.com/showthread.php/2256-Engine-management
https://www.euroga.org/forums/maint...ter-applicable-to-our-aircraft-engines?page=1

 

[asicer]

How exactly does one maintain 75% or greater power? Full throttle at or below what altitude?

3% power loss per 1000 ft of altitude is the general rule. So to maintain 76% power, you'll want to lose less than 24% so stay below 8000 ft, if your engine is following the generality.

 

[FORANE]

3% power loss per 1000 ft of altitude is the general rule. So to maintain 76% power, you'll want to lose less than 24% so stay below 8000 ft, if your engine is following the generality.

What about RPM's?

 

[Gary Ward]

What about RPM's?

Look in your POH for the rpms for 75% power.

I'd fly it for 2 hours at 75% and then 30 minutes at wide open throttle.
Then fly the 2nd flight for 2 hours at 65-75% power and then the last 15-20 minutes at wide open throttle.

I broke in a new motor last year and this is lycomings suggestions.
First they recommended 10 minutes at 1000 rpms with the cowl off to check for leaks. Then 20 minutes with the cowl on facing the wind at 1500 rpms on the ground. I shut it off and let it cool. Then I taxied to the runway and took off without delay.

My motor took about 5 hours to seal up/break in. I flew at 3000'.

You need to remove the pistons to dissolve the carbon so the new rings can float in the ring groove. Also check the ring groove for the proper clearance. The piston is carboned up from the broken ring, been like that for a while.

Rings can break from improper installation(not enough end gap) and most times from detonation, too lean of mixture, and from closing the throttle all the way abruptly. Always leave the throttle open a little on descents
The ring did not break from carbon.
I would only use WD40 on the cly walls and the rings for break in. But I would read up exactly what your type rings and cly walls need and follow those directions exactly. The wrong lube will keep the new rings from seating and that is what it sounds like happened the first time. I highly recommend to follow the manufactures instructions and not from us. It sounds like the clys need to be re honed also.

Good luck with it.

 

[Gary Ward]

This is what a piston should look like at 1700 hours and the rings mostly sealing. Your piston is showing a lot of dirt when assembled. Could affect ring seating?

Fly it at 2500 rpms for 2 hours and then WFO for 30 minutes. Then for 2 more hours at 2350-2500 rpms and then WFO for another 20 minutes. My motor used one qt first 2.5 hrs. and 3/4 of a qt the second flight. Then it stopped using oil and was broke in. I have 320 hrs on it now since July 2020.
I put the above motor back together and flew it another 100 hours, then swapped in this new motor that I did the official break in on it.

https://www.lycoming.com/content/hard-facts-about-engine-break

 

[FORANE]

“ Limit ground runs” can include towing rather than a downwind taxi.

I did this today. Thanks for the suggestion.

Flew it around 350 nm. Tried to stay at 75% power as recommended by Titan. Discovered that breaking in a top might not be a good idea in rough air. At 3,000 msl and 75% power I was indicating 185 kts which is well into the yellow arc.